Ecology of Root Nodule Bacterial Diversity: Implications for Soybean Growth

• Main Author: Sharaf, Hazem
• Other Authors: Genetics, Bioinformatics, and Computational Biology
• Format: Others
• Language: en
• Published: Virginia Tech 2021
• Subjects: Soybean; Bradyrhizobium; Biological Nitrogen Fixation; Pseudomonas; Drought; Sustainability; Nodule; Bacteriome; Diversity
• Online Access: http://hdl.handle.net/10919/106786

Doctor of Philosophy === Soybean, the top harvested crop in the USA and 4th worldwide, is an important protein input of the livestock industry and an affordable alternative protein source for human consumption. Soybean depends on Nitrogen (N), provided by bacteria helpers, diazotrophs, that reside in nodules on soybean roots, to synthesize protein. While N makes up 80% of air, it is not suitable in its breathable form for use by most living organisms. Diazotrophs, converts this N to ammonium, a form more useful by soybean, through a process called biological nitrogen fixation (BNF). Root nodules provide a special habitat to support BNF, where soybean provides the diazotrophs with carbon as an energy source in return for the fixed ammonium. BNF is sensitive to environmental stress such as drought, which in turn affects soybean yield. While synthetic fertilizer supplementation may help reduce yield loss, it contributes to global warming and water systems pollution. Understanding the associations between soybean and diazotrophs has the potential to improve the sustainable growing of soybean. In this dissertation, we first determine the changes in the soybean root nodule bacteria in response to different water treatments. We then study how the bacterial community inside the nodules change based on different rates of BNF. After that, we look for the connections between soybean-based nitrogen molecular markers and these bacteria. Finally, we take a deeper look at how some different types of bacteria can help support N fixation. Our results have revealed that soybean hosts non-nitrogen fixing bacteria, and in high abundances. These bacteria seem to be supporting soybean growth. However, the soybean-diazotroph relationship is more sensitive to changes in water. We also found variation in nodule bacterial diversity that is related to N fixation. As well, we found that these, previously undescribed, non-nitrogen fixing bacteria are capable of living inside the nodules and they could help support the diazotrophs, under certain conditions. We provide some possible explanations to how these, previously undescribed and novel, bacteria may have adapted to the nodules. These results are very useful in the development of new inoculation products that would serve as biofertilizers for soybean, thus improving the sustainability of the agriculture industry.